Asked whether there should be a public inquiry into the Skripal affair, Mrs Litvinenko told talkRADIO: "I'm sure, yes, because the public has to know what this investigation achieved and all information has to be provided.

"Because it would still be some kind of secret. But I believe secrets need to be stopped.

"People need to understand what happened. And this might prevent a future attempt."

'Were the lessons of Litvinenko learned?'

CCTV of the two men suspected of poisoning Sergei Skripal. Image: Metropolitan Police/PA

Asked for her reaction to the Skripal poisioning, Mrs Litvinenko said: "Of course it was a shock because after what we achieved in 2016 after the public inquiry report was released, and particularly after meeting Theresa May and her words: 'we will do everything (to ensure) such a crime will never happen again on British soil'.

"But when I received this news I realised something had happened again.

"The next question was: 'was enough done? Were the lessons of the Litvineko case learned?'

"And after that I realised it was not."

'Deliberately poisoned'

The 2006 murder of Mrs Litvinenko's husband was the subject of a public inquiry which concluded in 2016.

Former High Court Judge Sir Robert Owen produced a 300 page report that found Mr Litvinenko's death was 'probably' approved by Russian president Vladimir Putin.

Mt Litvinenko died in London from acute radiation syndrome three weeks after drinking tea containing polonium-210 at a Mayfair bar.

The inquiry report found that Mr Litvinenko has been deliberately poisoned by Andrei Lugovoi and Dmitry Kovtun.

Prime Minister Theresa May, who was Home Secretary at the time, initially refused requests to hold a public inquiry into Mr Litvinenko's death. She later relented.

'The public deserve to know'

Dr Andrew Foxall, Director of the Russia and Eurasia Studies Centre at the Henry Jackson Society, said: “It is only right that there should be a public inquiry into the poisoning of Sergei and Yulia Skripal, as well as the murder of Dawn Sturgess.

"The British public deserve to know how, twelve years after the murder of Alexander Litvinenko, two serving Russian military intelligence officers were able to enter the country undetected and carry out an attack with a proscribed chemical weapon in broad daylight.”